U.S. patent number 4,701,431 [Application Number 06/850,274] was granted by the patent office on 1987-10-20 for rare earth stabilized aluminum deficient zeolite.
This patent grant is currently assigned to Exxon Research and Engineering Company. Invention is credited to Lloyd A. Pine.
United States Patent |
4,701,431 |
Pine |
October 20, 1987 |
Rare earth stabilized aluminum deficient zeolite
Abstract
A rare earth stabilized aluminum deficient zeolite having the
structure of faujasite is provided. The zeolite is produced by
contacting a Y-type zeolite with a dealuminating agent to remove
aluminum from the crystal structure of the zeolite and ion
exchanging the zeolite with a specified amount of rare earth metal
cations to stabilize the aluminum deficient zeolite.
Inventors: |
Pine; Lloyd A. (Baton Rouge,
LA) |
Assignee: |
Exxon Research and Engineering
Company (Florham Park, NJ)
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Family
ID: |
27103679 |
Appl.
No.: |
06/850,274 |
Filed: |
April 10, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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685797 |
Dec 24, 1984 |
|
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560558 |
Dec 12, 1983 |
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Current U.S.
Class: |
502/73;
502/65 |
Current CPC
Class: |
B01J
29/084 (20130101); B01J 2229/16 (20130101) |
Current International
Class: |
B01J
29/00 (20060101); B01J 29/08 (20060101); B01J
029/06 () |
Field of
Search: |
;502/65,73 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dees; Carl F.
Attorney, Agent or Firm: Gibbons; Marthe L. Naylor; Henry
E.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part application of U.S.
patent application Ser. No. 685,797 filed Dec. 24, 1984, and now
abandoned which is a Rule 60 Divisional application of U.S. patent
application Ser. No. 560,558 filed Dec. 12, 1983, and now abandoned
the teachings of both of which are hereby incorporated by
reference. Also related is U.S. patent application Ser. No. 715,601
filed Mar. 25, 1985 and now abandoned which is a
continuation-in-part of U.S. patent application Ser. No. 560,558
now abandoned.
Claims
What is claimed is:
1. An aluminum deficient crystalline aluminosilicate zeolite having
the crystal structure of a faujasite and having a composition, in
its anhydrous state, in terms of mole ratio of oxides, as
represented by the following formula:
wherein RE represents a cation of a single rare earth metal or of a
mixture of rare earth metals, wherein "w" ranges from a value of
about 0.054 to about 0.217, said value w being the minimum amount
of rare earth in said zeolite needed to stabilize said aluminum
deficient zeolite; where R is an alkali metal cation; where M is
selected from the group consisting of hydrogen ion, ammonium ion
and mixtures thereof, wherein "a" ranges from zero to 1-3w; wherein
"b" ranges from zero to 1-3w; wherein a+b+3w=1; wherein Z ranges
from about 0.92 to 0.27, said value Z being the maximum fraction of
alumina in the crystal structure that can be removed, and wherein X
ranges from about 3.9 to about 54, said zeolite having a unit cell
size ranging from about 24.25 to about 24.75 Angstroms, said
zeolite having a unit cell size greater than the stoichiometric
unit cell size when measured after heating for two hours at
1300.degree. F., said zeolite falling within the area of FIG. 1
designated "stabilized zone".
2. The zeolite of claim 1 wherein said zeolite is composited with
catalytic metals of Group IB, IIA, IIB, IIIB, IVA, IVB, VB, VIB,
VIIB, VIII and mixtures thereof of the Periodic Table of
Elements.
3. The zeolite of claim 1 wherein X equals 3.9 and said unit cell
size is 24.75 Angstroms.
4. The zeolite of claim 1 wherein X equals 54 and said cell size is
24.25 Angstroms.
5. The zeolite of claim 1 wherein said zeolite is represented by
the formula:
6. The zeolite of claim 1 having been prepared by the steps which
comprise:
(a) contacting a Y-type zeolite with a dealuminating agent for a
time sufficient to remove at least about 5% of the aluminum atoms
from said zeolite;
(b) contacting the resulting dealuminized zeolite with a fluid
medium comprising rare earth metal cations to produce a rare earth
metal exchanged zeolite; and
(c) calcining the rare earth exchanged zeolite to produce said
aluminum deficient rare earth stabilized zeolite.
7. A method for the preparation of an aluminum deficient rare earth
stabilized crystalline aluminosilicate zeolite, which comprises the
steps of:
(a) treating an initial Y-type crystalline aluminosilicate zeolite
with a dealuminizing agent, said initial zeolite having the crystal
structure of faujasite and having a composition, in its anhydrous
state, in terms of mole ratios of oxides, represented by the
formula:
wherein R represents an alkali metal cation; wherein M is a cation
selected from the group consisting of hydrogen cation, ammonium
cation, and mixtures thereof; wherein a+b =1; wherein "a" ranges
from 0 to 1; wherein "b" ranges from 0 to 1; and wherein X ranges
from 3.9 to 54; said zeolite having a unit cell size ranging from
about 24.25 to about 24.75 Angstroms, said zeolite being treated at
conditions and for a time sufficient to remove at least 5 percent
of said aluminum from the structure of said zeolite;
(b) contacting said zeolite during step (a) or after step (a) with
an ion exchange medium comprising a rare earth metal cation to
replace at least a portion of said M or R cation with a rare earth
metal cation; and
(c) recovering an aluminum deficient rare earth stabilized
crystalline aluminosilicate represented by the formula of claim 1,
and having a unit cell size greater than the stoichiometric unit
cell size when measured after heating for two hours at 1300.degree.
F., and falling within the area of FIG. 1 designated "stabilized
zone".
8. The method of claim 7 wherein said dealuminating agent is
selected from the groups consisting of organic acids, inorganic
acids, chelating agents and mixtures thereof.
9. The method of claim 7 wherein step (a) is conducted at a
temperature ranging from 150 to 220.degree. F. to remove at least
about 5 percent of said aluminum from said crystal structure.
10. The method of claim 7 where said step (b) is conducted at a
temperature ranging from about 60.degree. F. to about 220.degree.
F.
11. The method of claim 7 wherein said initial zeolite has a silica
to alumina mole ratio ranging from about 3.9 to about 54 and a unit
cell size ranging from about 24.75 to about 24.25 Angstroms.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to rare earth metal stabilized-aluminum
deficient crystalline alumino-silicate zeolites, and methods for
their preparation.
2. Description of Information Disclosures
Crystalline aluminosilicate zeolites having a high silica to
alumina mole ratio may be prepared by various methods. High silica
to alumina mole ratio zeolites often have desirable characteristics
for use in certain processes. With some types of zeolites, it is
possible to control silica to alumina mole ratio during the
synthesis step. However, this does not work well for zeolites
having the same structure as natural faujasite. An example of such
a zeolite is zeolite Y. With these types of zeolite, it is usually
necessary to do some post-synthesis step in order to modify
significantly the silica to alumina mole ratio. One way to do this
is to add silica to the structure. A general method of doing this
involves exchange of alumina in the crystal structure (i.e.,
framework) of the zeolite for silica from an outside source. This
can be accomplished by treatment with ammonium-fluorosilicate as
described in U.S. Pat. No. 4,503,023. A second method uses
silicontetrachloride as the source of silica (H. K. Beyer and I.
Belenykaja, Catalysis by Zeolites, page 203, 1980, Elsevier
Scientific Publishing Company, Amsterdam). The older and more
typical way of increasing the silica to alumina ratio of the Y
zeolites involves some sort of dealumination. The literature on
these methods is often confusing as the term "dealumination" or
"alumina deficient" does not always have the same meaning. Several
different zeolites which are quite different but that have all been
described as "dealuminated" or "alumina deficient" are described in
more detail below:
1. In Case 1, the terms are used to describe the removal of alumina
from the zeolite structure by converting it from the tetrahedral
form required by the zeolite structure to an octahedral form. This
octahedral or non-zeolite alumina is not physically removed so the
silica to alumina ratio as measured by chemical analysis has not
changed but the silica-alumina ratio of the remaining zeolite has
increased. An example of this sort of dealumination is the
transformation of Y to an ultrastable Y zeolite (USY). The silica
to alumina mole ratio of the initial Y zeolite is usually near 4
whether measured by elemental analysis or some method that measures
the actual ratio in the zeolite crystal structure. After
hydrothermal treatment, the silica to alumina mole ratio in the
zeolitic crystal structure is typically about 8, but the silica to
alumina ratio as measured by elemental analysis has remained
unchanged. The determination of the silica to alumina mole ratio in
the zeolitic crystal structure is usually done by X-Ray
measurements of the unit cell size or by solid state nuclear
magnetic resonance measurements.
2. In a second case, the term "dealumination" is used to describe
the removal of the octahedral of non-zeolitic alumina such as
produced in Case 1 above further without removal of tetrahedral or
zeolitic alumina. For example, this can be done by chemically
treating a sample of zeolite that has already been transformed from
Y to ultrastable Y zeolite. The chemical treatment is kept mild
enough so that only the alumina that is not part of the crystal
structure of the zeolite will be removed. In this case, the silica
to alumina ratio as measured by chemical analysis will increase
while the silica to alumina ratio of the remaining zeolite as
measured by X-Ray diffraction or nuclear magnetic resonance will
not increase.
3. In Case 3, the term "dealumination" is both less precise and
more complicated because it describes situations where alumina is
removed both from the zeolitic crystal structure and at the same
time physically removing it from the sample of zeolite that is
being treated. Examples of ways of carrying this out usually
involve either some form of acid treatment or use of a complexing
agent such as ethylenediaminetetraacedic acid (EDTA). In this form
of dealumination, there is often a reordering of the zeolite
crystal structure. It is the degree to which this reordering takes
place that distinguishes several subcases of this type of
dealumination. This reordering of the zeolite crystal structure is
usually described as taking place by the migration of silicon atoms
from some other part of the zeolite to fill the defect sites or
hydroxyl "nests" left in the structure by the removal of the
aluminum atoms. In some cases, this reordering of the zeolite
crystal structure is deliberately encouraged by a post-treatment
with either heat or steam.
a. The most common subcase is that as the alumina is removed from
the zeolite crystal structure, the reordering takes place so that
the silica-alumina ratio in the crystal structure has been
increased by the same amount as the alumina that is chemically
removed.
b. In this subcase, the conditions are carefully controlled in
order to remove aluminum from the zeolite crystal structure so that
little or no reordering of the crystal takes place. In this case,
the empty sites or hydroxyl nests created by the removal of
aluminum atoms still remain. If no reordering has taken place and
the starting zeolite had no extraneous non-zeolitic alumina
present, the silica to alumina ratio as measured by the unit cell
size will not have changed but the silica to alumina ratio as
measured by chemical analysis will have increased. It is this type
of alumina deficient products that are the subject of this
invention.
c. The third subcase occurs frequently but may not always be
recognized. If the conditions of an acid treatment to remove
alumina from the structure are too severe, the zeolite structure
suffers partial collapse so that the remaining crystal structure
has a higher silica-alumina ratio as measured by magnetic nuclear
resonance or unit cell size than would be measured by chemical
analysis. This partial collapse is very similar to the
transformation of zeolite Y to an ultrastable Y zeolite.
There are several accepted techniques for measuring the silica to
alumina ratio in the zeolite crystal structure in the presence of
non-zeolitic silica or alumina. One of the newest methods is solid
state nuclear magnetic resonance which can distinguish between
aluminum atoms that are in a tetrahedral coordination, which is
required by the Y zeolite structure, or in an octrahedral
configuration which is typical of the alumina that is still present
but no longer part of the crystal structure of the zeolite. Another
and slightly less common method is the use of infrared spectroscopy
as described by Maxwell, et al. (Maxwell, I. E.; Van Earp, W. A.;
Hayes, G. R.; Couperus T.; Huis R.; and Clague, A. D. H., Journal
of The Chemical Society, Chemical Communications, 1982 p. 523). A
paper by Engelhard, et al. gives a good description of the NMR and
infrared techniques and compares the two methods relative to
chemical analysis (G. Engelhard, U. Lohse, V. Patzelovga, M. Magi,
and E. Lippmaa, Zeolites, Vol. 3, page 233, 1983). A third and
older technique is the use of X-Ray diffraction to measure the unit
cell size of the zeolite crystal. The unit cell size method depends
on the fact that a silicon-oxygen bond is shorter than that of an
aluminum-oxygen bond so that as alumina is removed from the crystal
structure and replaced by silica, there is an overall contraction
of the unit cell size which is directly proportional to the silica
to alumina ratio in the zeolite crystal structure. This technique
is described in U.S. Pat. No. 3,056,400 by Eberly, et al. and in
the work of Breck and Flannigan and in the Kerr U.S. Pat No.
3,442,795. The Kerr reference is particularly useful because, in
addition to pointing out the existence of hydroxyl "nests", it
discusses, in columns 15 and 16, the fact that aluminum atoms can
be removed from the tetrahedral sites of the zeolite without the
replacement by silicon atoms. This is an example of one of the
types of dealumination described earlier (subcase 3b) and it is in
this sense that the term "dealuminated zeolite" is used to describe
the products of this invention.
It is well known in the art that exchange of Y type zeolites with
rare earth metal ions increases both their thermal and hydrothermal
stability. The exact mechanism of this stabilization is still open
to speculation. The two most common theories cited in the
literature are as follows: (1) the rare earth metal ions, by virtue
of occupying exchange sites, slow down the rate that aluminum atoms
leave the zeolite crystal structure; (2) the physical presence of
the rare earth metal ions in the sodalite cage act to support
physically the sodalite structure which is a key building block of
the zeolite Y. Some evidence of the second mechanism is given in a
paper by Sherzer, et al. (Journal of Physical Chemistry, Vol. 79,
p. 1194, 1975). However, there is no suggestion in the prior art
that exchange by rare earth metal ions can stabilize a faujasite
type structure that contains a large number of hydroxyl nests that
have not been filled by silicon atoms. The present invention is
based on the finding that this particular form of alumina deficient
zeolite can be stabilized in this dealuminated state. The use of
rare earths to stabilize a Y or USY zeolite so that it retains this
alumina deficient structure in the presence of heat or steam has
not been reported in the prior art.
U.S. Pat. No. 3,442,795 discloses dealuminating a sodium Y zeolite
with ethylenediaminetetracedic acid complexing agent and then ion
exchanging the dealuminized zeolite with the rare earth
metal-containing solution. Most of the examples in this patent deal
with dealumination of the Y zeolites with ethylenediaminetetracedic
acid. The data given in Table E show an example of dealumination
where the aluminum is removed from the crystal structure and
physically from the zeolite without the reordering and the hydroxyl
"nests" being filled by silica atoms. This is shown by Examples 5,
6 and 7 where the silica to alumina mole ratio as measured by
chemical analysis increases from 5.8 to 9.12, while the unit cell
size or lattice constant remains essentially the same. This is also
shown in Examples 9 through 12 where a low silica to alumina sodium
Y zeolite was given a similar treatment. These two sets of examples
illustrate two other points that are also shown in the present
invention. First, the degree of dealumination that can be
accomplished without loss of crystallinity is dependent upon the
silica to alumina ratio of the starting material. A second point
illustrated by these data is that if dealumination is carried too
far, in addition to a loss in crystallinity, there will be a
spontaneous lowering of the unit cell size even under mild
conditions. This is shown by comparison of Example 8 with Example 7
and Example 13 with Example 12. Examples 20 and 21 of this patent
give examples of dealumination followed by rare earth exchange,
followed by a subsequent steaming. The final steaming conditions in
these examples are so severe that the zeolite crystal structure
could no longer be alumina deficient. These materials would fit
under Case 3a described above.
U.S. Pat. No. 3,506,400 discloses impregnating a dealuminized
zeolite with metal cations. The term "dealuminized" as used in this
patent involves the case where alumina is first removed from the
crystal structure by a steam treatment and then the amorphous
alumina that is still present in the sample is chemically removed
by treatment with a chelating agent or by acid extraction as in
Case 2 described earlier. In the examples given in Table 6 of this
patent where unit cell size data are available on the faujasite
type zeolites, there is no evidence that the procedures taught have
resulted in a material that contains hydroxyl "nests" or that the
zeolite crystal structures are alumina deficient. The products of
this patent would not be expected to be deficient in zeolitic
alumina. Eberly teaches a three step process that comprises a
partial removal of soda so that a critical heat-steaming step will
remove tetrahedral alumina from the zeolite crystal structure and
convert it to octrahedral or amorphous alumina. When alumina is
removed from the zeolite crystal structure by hydrothermal
treatment, the remaining structure recrystallizes to a higher
silica to alumina ratio. Hence, this new structure is believed to
be complete so that it does not have any defect sites that are
missing tetrahedral alumina atoms. The third step is an acid
leaching to remove the amorphous alumina that was created by the
hydrothermal treatment. (This is a Case 2 dealumination.)
U.S. Pat. No. 4,093,560 discloses dealuminizing an aluminum
silicate zeolite, which may be zeolite Y, with a solution
comprising an inorganic acid such as HCl and a salt of a complexing
agent such as ethylenediamenetetracedic acid. The dealuminized
zeolite is then ion exchanged with a solution of rare earth metals.
This patent teaches a special method of leaching alumina from a
zeolite that avoids the severe losses in zeolite stability that are
normally associated with a highly alumina deficient structure. The
teaching is to carry out the leaching at such a slow rate that
silicon atoms can migrate to fill the empty sites or hydroxyl
"nests" left in the structure by the leaving aluminum atoms (column
2, lines 45 to 49). This is analogous to the recrystallization of
the zeolite to a defect free structure of a higher silica to
alumina ratio achieved by hydrothermal treating such as was taught
by Eberly. The whole purpose of this special method of leaching is
to avoid a large formation of hydroxyl "nests" or defect sites
which would make the material less thermally stable. Note that in
Example 3 the mixture was stirred for two additional days after the
80 hour period during which acid had been added in the leaching
step. This is to allow time for the silicon atoms to migrate to
fill any empty sites left by the removal of aluminum atoms from the
zeolite crystal structure. In a publication in the Journal of
Physical Chemistry describing this same dealumination technique,
the products are shown to have improved thermal stability as
alumina is removed. This is further evidence that this method of
dealumination does not produce a structure containing a large
number of hydroxyl "nests" or defect sites. Hence, it is an example
of Case 3a dealumination.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided an aluminum
deficient crystalline aluminosilicated zeolite having the crystal
structure of a faujasite and having a composition, in its anhydrous
state, in terms of mole ratio of oxides, as represented by the
following formula:
wherein RE represents a cation of a single rare earth metal or of a
mixture of rare earth metals, wherein "w" ranges from a value of
about 0.054 to about 0.217, said value w being the minimum amount
of rare earth in said zeolite needed to stabilize said aluminum
deficient zeolite; where R is an alkali metal cation; where M is
selected from the group consisting of hydrogen ion, ammonium ion
and mixtures thereof, wherein "a" ranges from zero to 1-3w; wherein
"b" ranges from zero to 1-3w; wherein a+b+3w=1; wherein Z ranges
from about 0.92 to 0.27, said value Z being the maximum fraction of
alumina in the crystal structure that can be removed, and wherein X
ranges from about 3.9 to about 54, said zeolite having a unit cell
size ranging from about 24.25 to about 24.75 Angstroms, said
zeolite having a unit cell size greater than the stoichiometric
unit cell size when measured after heating for two hours at
1300.degree. F., said zeolite falling within the area of FIG. 1
designated "stabilized zone".
In accordance with the present invention, there is also provided a
method for the preparation of the above-described zeolites.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing unit cell size constant versus fraction
of structural alumina remaining in various zeolites.
FIG. 2 is a graph showing unit cell size versus mole ratio of
structural alumina to rare earth metal oxide.
FIG. 3 is a graph showing unit cell size versus calcination
time.
DETAILED DESCRIPTION OF THE INVENTION
The aluminum deficient rare earth metal stabilized crystalline
aluminosilicate zeolites of the present invention are Y-type
zeolites that have the crystal structure of faujasite and that have
a composition that can be represented in their anhydrous state, in
terms of mole ratios of oxides by the formula (1):
wherein R is an alkali metal and wherein "b" ranges in moles from 0
to 1-3w and wherein M is selected from the group consisting of
hydrogen ion, ammonium ion and mixtures thereof, and "a" ranges in
moles from 0 to 1-3w; and wherein RE represents a cation of a rare
earth metal. The rare earth metal cation may be a single rare earth
metal or a mixture of rare earth metals of elements having atomic
numbers ranging from 57 to 71. W ranges from 0.054 to 0.217 and
describes a minimum amount of rare earth metal cations that must be
present in the zeolite to stabilize the aluminum deficient anionic
crystal structure. To balance the electronic charges, "a"+"b"+3w=1.
The "w", minimum value of rare earth metal cations, varies as the
unit cell size varies from 24.25 to 24.75 Angstroms. The
relationship between "w" and unit cell size is given by the
equation (2):
In formula (1) of the composition of the zeolite, Z ranges from
about 0.92 to 0.27 and represents a maximum fraction of structural
aluminum, calculated as alumina (Al.sub.2 O.sub.3), that can be
removed to produce a zeolite of the present invention. The
relationship between Z and the unit cell size is given by equation
(3):
X ranges from 3.9 to about 54. The zeolite has a unit cell size
ranging from about 24.25 Angstroms to about 24.75 Angstroms. For
example, when X equals 3.9, the unit cell size is 24.75 Angstroms.
When X equals 54, the unit cell size is 24.25 Angstroms. A
preferred zeolite has the formula (4):
The aluminum deficient rare earth metal-stabilized crystalline
aluminosilicate zeolites of the present invention are more easily
described by referring to the figures. FIG. 1 describes three
zones. The top zone or prior art zone is the well known area where
rare earth metals are capable of stabilizing normal Y type zeolites
that are not alumina deficient in the crystal structure. The other
two zones are divided into a stabilized zone which contains the
zeolites of this invention and the non-stabilized zone which is
outside the limits of this invention. The line dividing these two
zones is described mathematically by equation 3. Note that this
line slopes such that materials of very low unit cell size or very
high silica to alumina mole ratio can have a larger fraction of
structural alumina removed and still be stabilized by subsequent
addition of rare earth metals. At the very high unit cell sizes,
which represent structures with low silica to alumina mole ratios,
only a small portion of the structural alumina can be removed and
still have a structure that can be stabilized by subsequent rare
earth metal exchange. The slope of this line is indicative of the
well known fact that high silica structures have higher thermal
stability, higher hydrothermal stability, and better tolerance to
acid than structures of lower silica content. This is analogous to
the slope of the line given in the figure in Kerr's U.S. Pat No.
3,442,795 where Kerr describes the percentage of alumina that can
be removed by his technique and still retain 50% crystal retention.
Note that the line shows that only a small amount of alumina can be
removed from the materials having very low silica to alumina ratios
and a much larger portion of alumina can be removed from materials
that start with a higher silica to alumina ratio. The zone bounded
by the line described by Equation 3 and the prior art zone
describes the amount of dealumination that we can achieve depending
on the starting material and still be able to stabilize the
material by subsequent rare earth exchange. FIG. 2 describes the
second critical limit on the zeolites of this invention. Again, the
figure is divided into a zone containing unstable materials and a
zone containing stable materials of this invention. The boundary is
a line that slopes according to the unit cell size. The equation
describing the line on this figure is the same as equation 2 on
page 4. This boundary simply recognizes the fact that even if one
is able to achieve the dealuminated material described in FIG. 1,
it will not be stable unless it has been exchanged with a certain
amount of rare earths. Again, it describes the fact that the higher
silica to alumina ratio materials, due to their inherent stability
even when dealuminated, require less rare earths to stabilize them
than the high unit cell size or low silica-alumina materials.
Hence, the zeolites of this invention are those that fall into the
stabilized zone as shown by FIG. 1 and have a high enough level of
rare earth metal exchange as shown in FIG. 2 to achieve
stabilization. Since both the amount of dealumination that can be
achieved and the required amount of rare earth metals are both a
function of the unit cell size of the starting materials, it makes
the molecular formulas describing these new and unconventional
materials more complex than usual.
The zeolites of the present invention have uniform pore diameters
ranging from about 6 to about 15 Angstroms, preferably from 6 to 10
Angstroms.
Various methods may be used to prepare the zeolites of the present
invention. A preferred method of preparation of the aluminum
deficient rare earth stabilized zeolites of the present invention
is as follows:
The initial crystalline aluminosilicate zeolite used as starting
material has a composition, in its anhydrous state, in terms of
mole ratios of oxides, that can be represented by formula (5):
wherein R represents an alkali metal cation and M is a cation
selected from the group consisting of hydrogen cation, ammonium
cation and mixtures thereof. The values a+b=1. The value "a" may
range from 0 to 1. The value "b" may range from 0 to 1.
The alkali metal cation may be a single alkali metal, such as
sodium or a mixture of different alkali metals; X ranges from 3.9
to 54. Thus, when X equals 3.9, the unit cell size is about 24.75
Angstroms; when X equals 54, the unit cell size is about 24.25
Angstroms. The unit cell size of the initial zeolite may range from
about 24.25 to about 24.75 Angstroms. The initial zeolite has the
crystal structure of faujasite and is a Y-type zeolite which may
have been derived from a naturally occurring zeolite or a
synthetically prepared zeolite. Zeolite Y is described in U.S. Pat.
No. 3,120,017.
As a specific example of an initial zeolite, a NaY or a NaHY
zeolite having a silica to alumina mole ratio ranging from about 4
to about 10 is contacted with a dealuminating agent for a time
sufficient to remove at least about 5 percent, preferably 10
percent, more preferably from about 20 to about 40 percent of the
aluminum atoms present in the anionic framework (i.e., crystal
structure) of the initial zeolite. The dealuminating agent may be
inorganic acid, or organic acid, a chelating agent or mixtures
thereof.
Suitable inorganic acids include hydrochloric acid, sulfuric acid,
and nitric acid.
Suitable organic acids include monocarboxylic acids, and
polycarboxylic acids such as, for example, formic acid, acetic
acid, trichlorocetic acid, trifluoroacetic acid, oxalic acid,
malonic acid, succinic acid, citric acid, gluconic acid and
tartaric acid. Some of these acids also act as chelating agents.
The concentration of the acid is suitably maintained such that the
pH of the dealuminating agent-zeolite mixture is usually greater
than about 3, preferably between about 2 and about 5. The lower end
of the pH of the acid solution is limited by the silica to alumina
ratio of the starting material. High silica to alumina (i.e., low
unit cell) starting materials can tolerate low pH limits without
loss of crystal structure.
Suitable chelating agents or complexing agents include materials
which form a complex with aluminum such as
ethylenediaminetetraacetic acid, and derivatives thereof, such as
diethylene triamine pentaacetic acid, nitrilotriacetic acid. The
acid and chelating or complexing agent can be used in
combination.
The initial zeolite is contacted with the dealuminating agent at a
temperature ranging from about 150.degree. to about 220.degree. F.,
preferably from about 180.degree. to about 210.degree. F. for a
period of time ranging from about 0.5 to about 8 hours. The
reaction is normally conducted at atmospheric pressure; however,
high pressures could be utilized, especially when it is desired to
use higher temperatures and shorter time.
Simultaneously with the dealuminating agent or after the
dealuminating step, the initial or dealuminated zeolite is
contacted with a fluid medium comprising rare earth metal cations
of a single rare earth metal or of a mixture of rare earth metals,
herein designated "RE", to ion exchange (replace) at least a
portion, preferably substantially all of the cations of the initial
zeolite with rare earth metal cations. The rare earth metal cation
exchange is conducted at conditions and for times sufficient to
produce a zeolite having the rare earth metal content that will
stabilize the aluminum deficient zeolite and fit the formula given
herein for new aluminum deficient rare earth exchanged zeolites.
The medium comprising the rare earth metal cations is typically a
rare earth metal salt added to an aqueous solution, such as salts
of cerium, lanthanum, praseodymium, neodymium, promethium,
samarium, europium, gadolinium, terbium, dysprosium, holmium,
erbium, yttrium, thulium, scandium, lutecium and mixtures
thereof.
The concentration of the rare earth metal cations used would
generally be in excess of the number of cations needed to exchange
theoretically all of the exchangeable cations of the zeolite with
rare earth metal cations. Suitable rare earth ion exchange
conditions include a temperature ranging from about 60.degree. to
about 220.degree. F., preferably from about 150.degree. to about
200.degree. F., and a time ranging from about 0.5 to about 4 hours,
that is, a time sufficient to provide at least the minimum amount
of rare earth metal cations required to stabilize the zeolite. The
pressure is not critical. Typically, the ion exchange is conducted
at atmospheric pressure although superatmospheric pressures or
subatmospheric pressures may be used.
The aluminum deficient rare earth stabilized crystalline
aluminosilicate is recovered from the ion exchange medium by
filtration, washed with water, dried at a temperature ranging from
about 180.degree. to about 250.degree. F., calcined at a
temperature ranging from about 800.degree. to about 1200.degree. F.
The aluminum deficient rare earth stabilized crystalline
aluminosilicate zeolites of the present invention prepared by the
above-described method fall within the region in accompanying FIG.
1 designated "stabilized zone". In FIG. 1, the unit cell size
constant in Angstroms is plotted against 1-Z, which is the fraction
of structural aluminum or alumina remaining. By the term
"stabilized" with reference to the zeolite is intended herein that
the aluminum deficient zeolite has improved ability to retain its
crystal structure and that it has improved resistance to changes in
unit cell size in the presence of steam and heat. Furthermore, the
aluminum deficient zeolites of the present invention, after heating
for either 2 hours at 1300.degree. F. or 1 hour at 1500.degree. F.,
still retain this alumina deficient state. FIG. 2 shows that the
higher the unit cell size the more rare earth metal cations are
needed for stabilization.
The new zeolites of the present invention may be used alone as
catalysts or sorbents. Furthermore, they may be used as catalyst
components, sorbent components, catalyst support, or sorbent
support by compositing them with sorption active materials or
catalytic materials, for example, with materials which function as
hydrocarbon treating, including conversion, catalysts in such
processes as cracking, hydrocracking, isomerization,
polymerization, disproportionation, demetallization, hydrogenation,
including aromatics hydrogenation, hydrodesulfurization,
hydrorefining, denitrogenation, etc. The zeolites of the present
invention may be composited with known catalytic metals and
compounds of metals of Groups IB, IIA, IIB, IIIB, IVA, IVB, VB,
VIB, VIIB, and VIII and mixtures thereof of the Periodic Table of
Elements as given in the Handbook of Chemistry and Physics
published by Chemical Rubber Company, Cleveland, Ohio, 46th Ed.,
1964. The catalytically active metals and metal compounds may be
combined with the zeolites of the present invention in any way
known in the art, such as by ion exchange, by vapor phase
deposition, impregnation, at any suitable stage of the zeolite
preparation, including before or after calcination of the zeolite.
The zeolites of the present invention may also be composited with
non-metal catalytic components, inert materials, supports such as
inorganic oxides, for example, silica, silica-alumina, alumina,
zirconia, magnesia, titania; clay; acid treated clays, carbon. When
the zeolite is used with other catalytic or inert materials, the
zeolite may be used as a composite particle or the zeolite may be
used as a physical mixture of separate particles of the zeolite and
particles of the other catalytic or inert component.
The operating conditions to be employed in the present invention
are well known and vary with the particular reaction desired. Table
"A" summarizes typical reaction conditions effective in the present
invention.
TABLE "A" ______________________________________ Principal
Temperature, Total Reaction Desired .degree.F. Pressure, psig
______________________________________ Hydrorefining 500-900
50-2000 Hydrodesulfurization 600-900 60-3500 Hydrocracking 400-900
200-3000 Catalytic Cracking 700-1300 0-150 Catalytic Reforming
850-1000 50-1000 ______________________________________
The catalyst or sorbent of the present invention may be disposed in
the reaction zone as a fixed bed, ebullated bed, fluid bed,
transfer line (suspension), moving bed or slurry of particles in
the feed, etc. The feedstocks suitable for use in the process of
the present invention include any of the well known feeds
conventionally used in the particular process. Thus, in hydrocarbon
treating and conversion processes, the hydrocarbonaceous feed may
be derived from any source such as petroleum, shale, tar sand, coal
liquefaction products, including coal liquefaction bottoms and
mixtures thereof. The zeolites of the present invention are
particularly well suited for use in catalytic cracking of
hydrocarbons.
PREFERRED EMBODIMENTS
The following examples are presented to illustrate the
invention:
COMPARATIVE EXPERIMENT
In this comparative experiment, the zeolite starting material was a
low soda type Y zeolite containing less than 4.0 weight percent
Na.sub.2 O per total zeolite, herein designated Zeolite No. 1. A
solution was made by dissolving 272 gms of ammonium chloride and 92
ml of concentrated hydrochloric acid in 2400 ml of water. 180 ml of
a solution containing the concentrated chlorides of a commercially
available rare earth mixture was added to the above solution. The
concentration of this rare earth chloride solution was equivalent
to 484 gms of RE.sub.2 O.sub.3 /liter. 463 gms of Zeolite No. 1
were then stirred into the rare earth-acid solution. The mixture
was heated to 180.degree.-190.degree. F. and stirring was continued
for 2 hours. The zeolite was recovered by filtration and the wet
cake divided into two equal portions. One half was washed by
stirring for 30 minutes in 2400 ml of hot water. After filtering
and drying at 250.degree. F., this material was labeled 1A. The
other half of the wet cake was given a second two-hour treatment at
180.degree.-190.degree. F. with a solution made from 46 ml of
concentrated hydrochloric acid, 136 gms ammonium chloride and 90 ml
of the same rare earth chloride solution all dissolved in 1200 ml
of water. This sample, 1B, was filtered, washed, and dried the same
as for sample 1A above. The inspections on samples 1A and 1B are
compared in Table I with those for the Zeolite No. 1 starting
material. It can be seen that in both cases considerable alumina
was leached from the Zeolite No. 1 starting material without
significantly changing the cell constant. The thermal stability of
samples 1A and 1B was determined by heating a small part of each
sample and measuring the cell constant on the treated sample. In
both cases there was considerable shrinking of the crystal
structure. These samples are not fully rare-earth exchanged to the
required level so they are not well stabilized and are not
materials of this invention.
TABLE I ______________________________________ Zeolite Sample No. 1
1A 1B ______________________________________ Chemical Anal., Wt. %
SiO.sub.2 72.2 70.45 78.1 Al.sub.2 O.sub.3 24.8 21.34 17.6 RE.sub.2
O.sub.3.sup.(1) 0 5.20 2.16 Na.sub.2 O 2.50 1.91 1.29 SiO.sub.2 to
Al.sub.2 O.sub.3 ratio 4.94 5.61 7.54 Physical Properties Cell
Constant, .ANG. (dried at 250.degree. F.) 24.70 24.70 24.68 X-Ray
Crystallinity, % 183 170 143 Al.sub.2 O.sub.3 deficiency, % 0 12 34
Cell Constant After Heating, .ANG. 2 Hrs @ 1300.degree. F. -- 24.60
24.52 2 Hrs @ 1400.degree. F. -- 24.63 24.57 1 Hr @ 1500.degree. F.
-- 24.60 24.52 ______________________________________ .sup.(1)
RE.sub.2 O.sub.3 denotes rare earth metal oxide.?
EXAMPLE 1
The samples from the comparative experiment described above were
converted into the materials of this invention by further treating
them with rare earth chloride solution. Sample 1A was stirred into
1000 ml of water to which 25 cc of the mixed rare earth chloride
solution described in the comparative experiment had been added.
The mixture was heated to 150.degree. F. and stirred for 3 hours.
The zeolite was removed from the rare earth solution by filtration
and washed by stirring for 30 minutes in 800 ml of hot water. After
filtering and drying at 250.degree. F., the sample was labeled 2A.
Sample 1B was treated in the same manner to produce sample 2B. The
inspection on these samples are given in the table below along with
the cell constants measured after a standard heat treatment. It can
be seen that the cell constants of these samples were changed very
little by the heat treatment.
TABLE II ______________________________________ Sample 2A 2B
______________________________________ RE.sub.2 O.sub.3, Wt. %
11.60 10.3 X-Ray Crystallinity, % 194 131 Cell Constant After
Heating, .ANG. 2 Hrs @ 1300.degree. F. 24.67 24.69 2 Hrs @
1400.degree. F. 24.68 24.69 1 Hr @ 1500.degree. F. 24.67 24.66
______________________________________
Samples 2A and 2B are zeolites in accordance with the present
invention.
EXAMPLE 2
A sample of a Y type zeolite synthesized so as to have a high
SiO.sub.2 -Al.sub.2 O.sub.3 ratio, herein designated Zeolite No. 3,
was converted into the material of this invention by giving it the
identical treatments used to produce samples 2A and 2B. The
analytical measurements and its thermal stability are given in the
table below. It can be seen that in the case of sample 3B, so much
alumina was removed from the crystal structure that it collapsed
and became mostly amorphous material. Sample 3A is a zeolite in
accordance with the present invention.
TABLE III ______________________________________ Starting Sample
Zeolite No. 3 3A 3B ______________________________________ Chemical
Analysis, Wt. % SiO.sub.2 81.1 85.5 92.4 Al.sub.2 O.sub.3 16.3 11.2
5.4 RE.sub.2 O.sub.3 0 3.14 1.83 Na.sub.2 O 1.47 .12 .01 SiO.sub.2
/Al.sub.2 O.sub.3 8.46 12.98 29.1 Physical Properties Unit Cell,
.ANG. (dried at 250.degree. F.) 24.51 24.49 24.38 Crystallinity, %
311 235 28.6 Al.sub.2 O.sub.3 deficiency, % -- 35 71 Unit Cell
After Heating, .ANG. 2 Hrs @ 1300.degree. F. -- 24.46 -- 1 Hr @
1400.degree. F. -- 24.48 -- 1 Hr @ 1500.degree. F. -- 24.49 --
______________________________________
EXAMPLE 3
In this example, the zeolite starting material was a low soda
ultrastable Y zeolite having a unit cell size below 24.55 .ANG.,
herein designated Zeolite No.4. Thirty pounds (dry basis) was
stirred for 2 hours at 180.degree.-190.degree. F. in a solution
made by dissolving 30 lbs of ammonium sulfate and 3.68 liters of
concentrated hydrochloric acid in 200 lbs of water. The solid was
removed by filtration and the wet cake washed by reslurrying in 150
lbs of hot water for about 20 minutes. The solid was recovered by
filtration and the wet cake divided into two equal portions. One
portion was dried at 250.degree. F. and labeled 4A. One portion was
further extracted by stirring for 2 hours at 190.degree. F. in a
solution made by dissolving 15 lbs of ammonium sulfate and 1840 ml
of concentrated hydrochloric acid in 100 lbs of water. The solid
was recovered by filtration and the wet cake washed with 3-8 lb
portions of hot water. The material was further washed by stirring
for about 20 min. in 70 lbs of hot water. After filtering and
drying the solid was labeled 4B. The analytical inspections
obtained on these two samples are given in Table IV.
Since the Zeolite NO. 4 starting material used to make samples 4A
and 4B contained alumina in addition to that in the zeolite crystal
structure, the degree of alumina deficiency in the crystal
structure cannot be determined by direct chemical analysis. In
order to properly evaluate the effects of acid extraction, it is
necessary to distinguish whether the alumina being removed is
coming from the crystal structure of the zeolite or from some other
non-frame-work source. The most direct measure of the SiO.sub.2
/Al.sub.2 O.sub.2 ratio of the crystal lattice is the unit cell
constant determined by X-ray diffraction. These two parameters are
related by the equation developed by Breck and Flannigan that is
given below. By comparing the SiO.sub.2 /Al.sub.2 O.sub.3 ratio
from the cell constant with that from chemical analysis, it is
possible to decide whether the crystalline framework is alumina
deficient or whether the sample contains extra non-framework
octahedral alumina. ##EQU1##
If the structure is alumina deficient, it is possible to calcine it
in such a way that all of the defects or hydroxyl nests left in the
structure from the removal of tetrahedral alumina are closed so
that the cell constant is exactly that of the stabilized structure.
At this point, the SiO.sub.2 /Al.sub.2 O.sub.3 ratio calculated
from the cell constant will exactly match that of the crystal
structure. This unit cell size will be referred to as being the
"stoichiometric unit cell size." Further calcination starts to
remove alumina from the crystal structure to non-framework
positions with further lowering of the cell constant. It is
reasonable to expect that the rate of change in unit cell size
would be different for the two processes with the closure of the
voids being faster than the expulsion of alumina from framework.
Sample 4B was calcined under a variety of conditions and the unit
cell constant measured on the calcined samples. The data are
summarized in FIG. 3. The break in the curves at 24.44 .ANG. from
the 1100.degree. and 1200.degree. F. calcinations is taken to be
the stoichiometric unit cell size. Samples of 4A were treated in a
similar manner and the break in the curves was found at 24.45 .ANG.
showing that this material was less alumina deficient than sample
4B.
TABLE IV ______________________________________ Zeolite Sample No.
4 4A 4B ______________________________________ Chemical Analysis,
Wt. % SiO.sub.2 78.0 81.7 82.0 Al.sub.2 O.sub.3 23.7 17.9 14.6
Na.sub.2 O 0.15 0.12 0.11 SiO.sub.2 /Al.sub.2 O.sub.3 5.58 7.76
9.53 Physical Properties X-Ray Crystallinity, % 224 184 192 Cell
Constant After 24.52 24.52 24.48 Drying @ 250.degree. F.
Stoichiometric 24.51 24.45 24.44 Alumina Deficiency, % 0 26 17
Alumina Type, gms/100 gms SiO.sub.2 30.4 21.9 17.8 Total
Crystalline 20.2 15.7 15.1 Amorphous 10.2 6.2 2.7
______________________________________
Neither Sample 4A nor 4B is a zeolite in accordance with the
present invention. See example 4 where they are converted to
zeolites of the present invention.
Once the stoichiometric unit cell size has been determined, it is
possible to divide the alumina in each sample into crystalline
(zeolitic) alumina and amorphous (non-zeolitic) alumina. This is
done by subtracting the amount of the crystalline alumina
calculated from the stoichiometric unit cell constant from the
total amount of alumina, as determined by chemical analysis. Since
silica is not soluble in the acid solutions used to extract
alumina, it is convenient to account for the alumina by ratioing it
to a constant amount of silica. For uniformity, the alumina
deficiency in this and subsequent examples is based on the
difference in alumina content between the structures defined by the
stoichiometric cell constant and that for the dried sample. This
method accounts for the small amount of structural rearrangement
and partial loss of alumina deficiency that sometimes occurs
between acid extraction and rare earth exchange. Using the methods
described above, it was calculated that sample 4A was 26% alumina
deficient and that sample 4B was 17% alumina deficient. Even though
more total alumina was removed from sample 4B, the sample had
partially rearranged under reaction conditions as shown by the
lowering of the cell constant to 24.48 .ANG. with essentially no
change in X-Ray crystallinity. The net effect was that the percent
of alumina missing from the crystal structure is less for sample 4B
than for 4A where no such rearrangement took place.
EXAMPLE 4
Sample 4A was converted to the material of this invention by
exchanging it with rare earth ions. The sample (10 lbs dry basis)
was stirred into 60 lbs of water. The pH of the slurry was adjusted
to between 4.0 and 4.5 with dilute sulfuric acid and 2.5 liters of
the same rare earth chloride solution described in example 2 was
added. The mixture was heated to 135.degree. F. and stirred for 2
hours. The solid was removed by filtration and then given a second
two hour rare earth exchange under the same conditions as above.
The solid was recovered by filtration and washed by stirring in 50
lbs of hot water for about 20 minutes. The material was filtered,
dried at 250.degree. F. and labeled sample 5A. Sample 4B was
treated in an identical manner to produce sample 5B. The
inspections on these samples are given in the table V along with
the cell constants measured after the standard heat treatment. In
both cases, the cell constants show that rare earth exchange
stabilized the structure in an alumina deficient state.
TABLE V ______________________________________ Sample 5A 5B
______________________________________ RE.sub.2 O.sub.3, Wt. % 6.88
6.46 X-Ray Crystallinity, % 107 112 Cell Constant After Heating,
.ANG. 2 Hrs @ 1300.degree. F. 24.47 24.51 1 Hr @ 1400.degree. F.
24.50 24.51 1 Hr @ 1500.degree. F. 24.47 24.49
______________________________________
Sample 5A and Sample 5B are zeolites in accordance with the present
invention.
EXAMPLE 5
This example shows that almost complete rare earth exchange of the
alumina deficient structures is required to achieve stabilization.
Small portions of sample 4B were treated as in example 1, except
that lesser amounts of rare earth were added to the ion exchange
solutions. These samples are compared in Table VI with sample 5B.
It can be seen that the lower levels of rare earths are not
adequate to stabilize the structure in an alumina deficient
state.
TABLE VI ______________________________________ Sample 5B 6A 6B
______________________________________ RE.sub.2 O.sub.3, Wt. % 6.46
2.06 0.93 Cell Constant After Heating, .ANG. 2 Hrs @ 1300.degree.
F. 24.51 24.46 -- 1 Hr @ 1400.degree. F. 24.51 24.45 24.45 1 Hr @
1500.degree. F. 24.49 24.43 24.40
______________________________________
The zeolites of Sample 6A and 6B are not in accordance with the
present invention.
EXAMPLE 6
A sample of a Y-type zeolite synthesized to have a high SiO.sub.2
/Al.sub.2 O.sub.3 ratio having a silica to alumina ratio of
10.95:1, herein designated zeolite No. 7, was converted to the
material of this invention by using the acid extraction and rare
earth exchange procedures given in Examples 3 and 4. The zeolite
starting material contained no amorphous alumina as shown by the
fact that the silica/alumina ratio found by chemical analysis is in
good agreement with that calculated from the cell constant. Since
the starting material contained no amorphous alumina and the cell
constant measured on sample 7A showed no shrinkage due to the acid
extraction, the alumina deficiency of sample 7A can be calculated
from either the chemical analysis or from the stoichiometric and
dried unit cell sizes. As shown in Table VII, the agreement between
the two calculation methods is within the precision of the
analytical data on which they are based.
TABLE VII ______________________________________ Starting Sample
Zeolite No. 7 7A 7B ______________________________________ Acid
Treatments None One Two Chemical Analysis, Wt. % SiO.sub.2 83.7
91.2 94.0 Al.sub.2 O.sub.3 13.0 11.2 5.2 Na.sub.2 O 0.49 0.07 0.004
SiO.sub.2 /Al.sub.2 O.sub.3 10.95 13.84 30.73 Physical Properties
Crystallinity, % 287 308 125 Unit Cell, .ANG. 24.45 24.45 24.31
After Drying At 250.degree. F. Stoichiometric 24.44 24.38 24.25
Alumina Deficiency, % By Chemical Analysis 0 23 -- By Unit Cell
Measurement 0 30 50 Rare Earth Exchanged 3.08 2.38 RE.sub.2
O.sub.3, Wt. % Unit Cell Size After Heating, .ANG. 2 Hrs @
1300.degree. F. -- 24.46 24.35 1 Hr @ 1400.degree. F. -- 24.49
24.35 1 Hr @ 1500.degree. F. -- 24.47 24.34
______________________________________
Samples 7A and 7B are zeolites of the present invention.
EXAMPLE 7
In this example, the low soda Y zeolite, No. 1, was calcined for 90
minutes at 1200.degree. F. prior to being acid extracted. The
calcined zeolite had a cell constant of 24.57. The calcined zeolite
was then given a single acid extraction using the same procedure as
that used for preparing 4A and then rare earth exchanged using the
same procedure as that used for converting sample 4A to sample 5A.
The inspections and thermal stability of the product, Sample 8, are
shown in Table VIII.
TABLE VIII ______________________________________ Sample 8
______________________________________ Chemical Analysis, Wt. %
SiO.sub.2 75.9 Al.sub.2 O.sub.3 18.5 Na.sub.2 O 0.40 RE.sub.2
O.sub.3 7.13 Physical Properties 127 X-Ray Crystallinity, % Cell
Constant, .ANG. Dried at 250.degree. F. 24.57 Stoichiometric 24.49
Al.sub.2 O.sub.3 Deficiency, % 26 Unit Cell Size After Heating,
.ANG. 2 Hrs @ 1300.degree. F. 24.53 1 Hr @ 1400.degree. F. 24.53 1
Hr @ 1500.degree. F. 24.54
______________________________________
* * * * *